1. Field of the Invention
This invention relates to an NC data creation method and, more particularly, to a method of creating NC data for simultaneous five-axis control in which a character or pattern is cut into a curved surface using tool nose position data and data indicating the orientation of the central axis of the tool.
2. Description of the Related Art
In cutting a curved surface by simultaneous five-axis control, movement is possible simultaneously along five axes, namely an X axis, Y axis, Z axis, a horizontal rotation axis (B axis) and a vertical rotational axis (C axis), and NC data for such simultaneous five-axis control is created in such a manner that the vector of the central axis of the tool will point in the normal direction at each point on the curved surface. More specifically, the NC data for simultaneous five-axis control are created by finding a sequence of points on a sculptured surface for specifying tool nose position, obtaining normal vectors at the sequence of points on the curved surface, calculating the position (x,y,z) of the center of rotation of the tool, as well as the positions (b,c) of horizonal and vertical rotation, by a well-known computation based on the normal vector and tool nose position (X,Y,Z), and using x, y, z, b, and c to create the data. For example, see U.S. Pat. No. 4,559,601 (entitled "Numerically Controlled Cutting Method").
There are cases where edge removal or the carving of a character or pattern on a curved surface is performed by a five-axis processing machine. In such cases, since cutting is performed with the central axis of the tool inclined in the direction of the normal line at all times in accordance with the prior-art method, the cut section (cross section) CS is monotonous, as shown in FIG. 10(a), and cutting which will give the impression of hand-carving cannot be performed by freely designating the angle of the central axis of the tool, as shown in FIG. 10(b). In FIG. 10, SS denotes a sculptured surface, TL a tool and CS the cut section.